1. Field of the Invention
The present invention relates to a polysilicon production apparatus and method, and more specifically to an apparatus and method for the production of polysilicon using a horizontal reactor.
2. Description of the Related Art
In recent years, there has been a growing demand for polysilicon as a raw material in the fabrication of electronic devices, such as semiconductor devices and photovoltaic devices. Many methods are known for the production of silicon as a raw material in the fabrication of semiconductors or solar photovoltaic cells and some of them are have already been carried out industrially.
Currently commercially available high-purity polysilicon is typically produced by chemical vapor deposition processes. Specifically, polysilicon can be produced by reacting trichlorosilane gas with a reducing gas, such as hydrogen gas, as depicted in Reactions 1 and 2:SiHCl3+H2→Si+3HCl  (1)4SiHCl3→Si+3SiCl4+2H2  (2)
The Siemens method is an exemplary commercially available polysilicon production method. According to the Siemens method, silane gases as reactant gases and hydrogen gas as a reducing gas are fed into a bell-jar reactor and a silicon rod placed in the bell-jar reactor is heated to or above the deposition temperature of silicon. When transferred to the reactant gases and the reducing gas, the heat reduces the reactant gases to deposit polysilicon.
However, the Siemens reactor consumes much energy, commonly an electrical energy of about 65 to about 200 KWh/kg. This electrical energy cost accounts for a very large portion of the total polysilicon production cost. Another problem is that the batch type deposition requires extremely laborious processes, including silicon rod installation, ohmic heating, deposition, cooling, extraction, and bell-jar reactor cleaning.
Another method is associated with the deposition of polysilicon using a fluidized bed. According to this method, a silane is supplied simultaneously with the supply of fine silicon particles having a size of about 100 microns as deposition nuclei to deposit silicon on the fine silicon particles, and as a result, silicon grains having a size of 1 to 2 mm are continuously produced. This method is advantageous in that continuous operation is possible for a relatively long time. However, due to its low deposition temperature, monosilane as a silicon source is thermally decomposed even at a low temperature, tending to form finely-divided silicon or deposit silicon on the reactor wall. Thus, regular cleaning or exchange of the reaction vessel is required.
An apparatus for producing polycrystalline silicon using a vertical reduction reactor is disclosed in Korean Patent No. 10-0692444. The apparatus uses a heater on which silicon is deposited. The heater is cylindrically shaped for high thermal efficiency. Specifically, the apparatus includes (a) a cylindrical vessel having an opening which is a silicon take-out port at the lower end, (b) a heater for heating the inner wall from the lower end to a desired height of the cylindrical vessel at a temperature equal to or higher than the melting point of silicon, (c) a chlorosilane feed pipe which is composed of an inner pipe having a smaller outer diameter than the inner diameter of the cylindrical vessel and constituted such that one opening of the inner pipe faces down in a space surrounded by the inner wall heated at a temperature equal to or higher than the melting point of silicon, and (d) a first seal gas feed pipe for supplying seal gas into a gap defined by the inner wall of the cylindrical vessel and the outer wall of the chlorosilane feed pipe. The apparatus optionally further includes (e) a hydrogen gas feed pipe for supplying hydrogen gas into the above cylindrical vessel.
FIG. 1 schematically illustrates a polysilicon production apparatus that is of a vertical reduction reactor type.
Referring to the figure, the polysilicon production apparatus includes a reactant gas inlet port 11 disposed on top of a reactor 10, a vacuum pipe 12 disposed at one side of a middle portion 10b of the reactor 10, and an outlet pipe 13 disposed at the other side of the reactor 10. Units for collecting, cooling, and casting molten silicon are disposed in a lower portion 10c of the reactor 10.
Silane gases as reactant gases are supplied through the inlet port 11. The silane gases may be monosilane, dichlorosilane, trichlorosilane (TCS) or tetrachlorosilane (STC). After operation of the reactor 10, the vacuum pipe 12 can be used to create a vacuum for cleaning and purging the internal space of the reactor and the outlet pipe 13 can be used to release waste gases generated during the reactions. An induction heating coil 14 is provided in an upper portion of the reactor 10. When an RF current is applied to the induction heating coil 14, an eddy current is generated in a reaction tube 21 to release heat. This heat is applied to the gases entering through the gas inlet port and the wall surface of the reaction tube 21 to induce the deposition of polysilicon.
FIG. 2 is a schematic cross-sectional view of the upper portion 10a of the reactor illustrated in FIG. 1.
Referring to the figure, the reaction tube 21 is provided in the upper portion 10a of the reactor and the reactant gases, such as silane gases, are supplied to the reaction tube 21 through the reactant gas supply port 11. A heating coil 23 is arranged on the surface of an insulating tube 22 provided outside the reaction tube 21. A sealing gas is supplied through a sealing gas supply pipe (not shown) and is filled between the reaction tube 21 and the insulating tube 22 and between the insulating tube 22 and an outer vessel 26. The sealing gas 25 serves to prevent the reactant gases from leaking through gaps between the reaction tube 21 and the insulating tube 22 and between the insulating tube 22 and the outer vessel 26. A reducing gas, such as hydrogen, is supplied through a reducing gas supply pipe (not shown). The reducing gas may be supplied in admixture with the silane gases.
As illustrated in the cross-sectional view of FIG. 2, the heating coil 23 is not wound in an upper region “A” of the reaction tube 21 but is wound in a lower region “B” of the reaction tube 21. This structure ensures thermal stability and substantially isothermal distribution of the reaction tube. The region “B” is required to have a length 3 to 4 times larger than the diameter of the reaction tube.
Thus, heat transferred from the heating coil 23 to the reaction tube 21 is concentrated on the lower region “B” rather than on the upper region “A”. However, the polysilicon production apparatus illustrated in FIGS. 1 and 2 has the problem that large amounts of the reactant gases and the reducing gas entering the reaction tube 21 pass through the reaction tube without coming into contact with the wall surface of the reaction tube 21, and as a result, sufficient deposition does not take place at high temperature.
That is, since heat is not sufficiently transferred to the gases flowing through the central portion of the reaction tube 21 farthest away from the heating coil 23, slow reduction reactions take place, leading to low overall production efficiency and energy efficiency.